S5 turbine housing with S4 turbo?
 

Anybody know if you can use the S5 turbine housing on S4 turbo, or are the turbine wheels different as well? I am aware they each take different manifolds, etc... Just wondering. Thanks.

The turbine housing is the only difference between the two.

^and wastegates. The s5 has a dual port waste gate while the s4 has a single. No matter what you do, make sure you port them!

Cool. Thanks guys...
I didn't think I needed to port the wastegate because I've had no boost creep issues. But after pulling my turbo and finding that the mani was only being held on by the two rear bolts that is probly why. It had to of been leaking.... I probly couldn't hear it over the rattle of the s4 exhaust flapper...

In most cases, the turbine housings can be swapped. But if you have an early S4 turbo, the CHRA will have a double heatshield on the back, which will not work with a late S4 or S5 housing. See step 5 in my rebuild thread: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/how-rebuild-stock-ht-18-turbo-build-hybrid-959045/

Can the 2nd heatshield be removed from an early S4 turbo and used with an S5 turbo exhaust housing? I missed the picture of the double heatshield in your thread, so I'm currently running an early S4 turbo with s5 hotside. :facepalm2: But I'm just running the turbo inefficiently, but not damaging anything correct?

I don't really feel like pulling the turbo again on a car with full emissions and A/C.

if the CHRA bolted down flat into the the turbine volute hen you have a later s4 turbo and its all OK
if you had the early s4 ( twin heat shields ) into a s5 volute then you will have the flanges pulled down at an angle as the chra will be 2mm too proud up out of the volute

to answer your question though,, yes you can remove the extra heat shield and re-assemble the turbo with no issue
( provided you mark the wheel orientation and use loctite and the angle TQ method to TQ the front nut )

Yes, that's exactly what I did for my hybrid. I had to take the freshly balanced S4 CHRA back apart to switch over to the single heatshield that was on my S5 turbo. I just marked the wheel/shaft/nut really well so I wouldn't have to rebalance the rotating assembly.

Didn't you notice the CHRA wouldn't go all the way flush with the turbine housing? Before I realized the difference, I torque the bolts all down to find the heads and flanges all sitting at an angle due to the 1mm height difference. Once I pulled the S5 turbo that was on the car & took it apart, it was clear that there were 2 different heatshield designs. Since your turbine is pulled back an extra ~1mm from the turbine housing (normal clearance is approx. 0.5 to 0.6mm), I'd expect it to spool up slower and potentially hold less boost in the high RPM range. But I couldn't see it hurting anything physically.

I spread the work out over a few weekends, but that was mostly due to problems adapting the hybrid parts. I have emissions and A/C as well.

^But you know what you are doing. :D Thanks for the input. I tried to rush the job and after shearing 4 of the bolts in the s4 hotside, it was S5 or nothing. Since the whole point of the s5 turbo swap is response, it's silly to leave it like this.

After looking at the pictures in your turbo rebuild thread, I see now I'm almost positive it's a double heatshield.

As for the housing not seating correctly, I had a similar issue when I pulled the exhaust housing to port the wastegate. I couldn't get it to seat quite right, but after tightening down the bolts/collars, it seated the housing just fine. I noticed the same thing as I put this s5 housing on and figured it'd do the same thing. I was focused on figuring out how to clock the s5 flange to the manifold and forgot to double check. Now I know. And knowing is half the battle!

Mine is an '88 A.E. So it is most likely the latest S4 style right?

I sheared one of the bolts when I was taking apart my S5 turbo to steal its housing. It had to be drilled out, but fortunately the threads were fine.

If your CHRA wasn't seating properly, maybe there was some rust or carbon buildup? I chipped a ton of carbon deposits out of the backside of the heatshields before putting it all back together. The one with a hot-side oil leak was really bad.

It should be fine (unless someone swapped the turbo at some point). The CHRA in my build thread is from the original turbo on my '87 TII. I don't remember the build date on it.

the early s4 turbo is quiet rare,, esp on the US continent as the majority of turbo engines went to japan or aus markets in 86/ early 87 before the US turbo release

usually the ID is easy cause the coolant banjo bolts are a size smaller

Apparently I own 3 of them. All with a 21mm hex head coolant banjo.

I measured the lip where the heatshield contacts the exhaust housings in case anyone wants to identify which version they have.

Double heat shield, early S4 ~= 5.7mm
Single heat shield, late S4 & S5 ~= 4.7mm